It has long been known that perishable foods can be preserved by drying, by salting and by acid-producing fermentations, and that chlorinated lime (calcium hypochlorite) can be used to deodorize sewage and garbage (and wounds). Sterilization denotes the use of either physical or chemical agents to eliminate all viable microbes from a material, while disinfection generally refers to the use of germicidal chemical agents to destroy the potential infectivity of a material. Sanitizing refers to procedures used to simply lower the bacterial content of utensils used for food. Antisepsis refers to the topical application of chemicals to a body surface to kill or inhibit pathogenic microbes. Disinfectants are widely used for skin antisepsis in preparation for surgery.
Sterilization of microbes exhibits the kinetics of a first-order reaction, in which the logarithm of the number of survivors decreases as a linear function of time of exposure.
Bacteria are the smallest organisms that contain all the machinery required for growth and self-replication. A bacterium includes a rigid cell wall surrounding the cytoplasmic membrane, which itself encloses a single naked chromosome without a nuclear membrane. The cytoplasmic membrane consists primarily of a bi-layer of lipid molecules.
The fundamental criterion of bactericidal action is loss of the ability of the organism to propagate indefinitely, when placed in a suitable environment. Bactericidal action suggests microbe damage of various types, including the triggering of irreversible damage to the cytoplasmic cell membrane or irreversible impairment of the DNA (or viral RNA replication. Accordingly, sterilization is not identical with destruction of microbes. Additionally, it is understood that damage to nucleic acids (DNA or RNA) is not always irreversible, as it is known that ultraviolet light-induced damage to viral nucleic acids can be repaired by enzymatic and genetic mechanisms.
Strongly acid and alkaline solutions are actively bactericidal. Indeed, the pH range tolerated by most microorganisms extends over 3 to 4 units, generally between pH values of about 4.5 to 8; however, mycobacteria are relatively resistant.
At sufficiently high concentrations, many chemicals are bacteriostatic and even bactericidal. The term disinfectant is restricted to chemical agents that are rapidly bactericidal at low concentrations. In contrast to lethal radiations--which damage the DNA (or viral RNA)--and to most bactericidal chemotherapeutic agents--which interact irreversibly with various active metabolic systems--most disinfectants act either by dissolving lipids from the cytoplasmic membrane (detergents, lipid solvents) or by damaging proteins (denaturants, oxidants, alkylating agents, and sulfhydryl reagents). The rate of killing by disinfectants increases with concentration and with temperature. Different kinds of disinfectants must be used for different purposes, due to the very large variety of microbes.
Chlorine has been used as an antiseptic for more than a century. Chlorine combines with water to form hypochlorous acid, a strong oxidizing agent. Hypochlorite solutions are used to sanitize clean surfaces in the food and the dairy industries and in restaurants; and Cl.sub.2 gas is used to disinfect water supplies and swimming pools.
Alkylating agents, e.g. ethylene oxide, replace the labile H atoms on --NH.sub.2 and --OH groups, which are abundant in proteins and nucleic acids (DNA, RNA), and also on --COOH and --SH groups of proteins. Indeed, ethylene oxide has proved to be the most reliable substance available for gaseous disinfection of dry surfaces. However, its use is more expensive and presents some hazard of residual toxicity (being mutagenic to bacteria and insects). Ethylene oxide is widely used to sterilize heat-sensitive objects: plasticware; surgical equipment; hospital bedding. These alkylating agents, in contrast to other disinfectants, are nearly as active against spores as against vegetative bacterial cells, because they can penetrate easily and do not require water for their action.
Cationic detergents, e.g. benzalkonium chloride, are known to be active against all kinds of bacteria. They act by disrupting the cytoplasmic membrane, causing release of metabolites (the cytoplasmic molecules of the cell); in addition, their detergent action provides the advantage of dissolving lipid films that may protect bacteria.
Fungi are similar to bacteria, yet one of their differences is that their nucleic acid, consisting of multiple chromosomes, is enveloped by a nuclear membrane. In some fungi (as in some bacteria), the cell wall is surrounded by an external capsular polysaccharide which, in the case of bacteria at least, protects the pathogenic microbe from phagocytosis and thus play a major role in determining virulence.
Spores are metabolic by-products in the life cycle of some bacteria and fungi, and are often very resistant to physical and chemical disinfectant agents. Spores contain one or several nuclei. Fungi produce a variety of exospores, including conidia, chlamydospores (thick-walled and very resistant), and sporangiospores. Bacteria produce endospores, i.e. sporeslocated within the cytoplasm of the parental cell.
Bacterial endospores are differentiated cells formed within a vegetative cell; they encase a genome in an insulating dehydrated vehicle that makes the cell ametabolic and resistant to various lethal agents, but permits subsequent germination in an appropriate medium. Spores are much more resistant than the parental (vegetative) cell to the lethal effect of heat, drying, freezing, toxic chemical s and electromagnetic radiations. Spores are formed by the invagination of a double layer of the cytoplasmic membrane, which closes off to surround a chromosome and a small amount of cytoplasm. A thin spore wall, and a thicker cortex with a much looser peptidoglycan, are synthesized between the two layers; outside the cortex is a protein coat, rich in disulfide cross-links and constituting up to 80% of the total protein of the spore. The keratin-like impervious properties of the coat account for the resistance to attack by deleterious chemicals, while the dehydration and the presence of a large amount of Calcium and dipicolinate contribute to the heat resistance.
A striking feature of spores is their huge content of Ca.sup.++, for which active transport units appear in the membrane of the mother cell early during sporulation. Normally the Ca.sup.++ is accompanied by a roughly equivalent amount of dipicolinic acid, which can chelate Ca.sup.++ ; dipicolinate is almost unique to bacterial spores and may constitute as much as 15% of their weight. Dehydration and ionic conditions are undoubtedly major factors in stabilizing spore proteins. Ca dipicolinate evidently plays a large role, by some as yet unknown mechanism, for its content markedly influences heat resistance. Recent research results point out to the control of calcium flow across the cytoplasmic membrane, thanks to a "calcium pump" assembly embedded into the bi-layer lipid membrane of cells and defining a calcium selective through-membrane channel ("The Cycling of Calcium as an Intracellular messenger", Scientific American, Oct. 1989).
A virus consists of a single nucleic acid (either DNA or RNA), and a protein shell or coat surrounding the nucleic acid; the complete viral particle is called a virion. Some viruses contain lipids and carbohydrates. Virions lack constituents fundamental for growth and multiplication, they never "grow": virions are by themselves metabolically inert. Virions multiply (replicate) only after cell-host invasion, and therefore are obligatory intracellular parasites. Hence, a virus is more than a simple nucleoprotein (a chemical substance), but not quite a microbe (a living entity); that is to say, a virus is not really "alive" as it is slightly short of the threshold of life as we define it.
Inactivation of virions is the permanent loss of infectivity. The exposure of a population of virions to a chemical (or physical) inactivating agent at a defined concentration for a limited time, results in the inactivation of a proportion of the virions; the others retain infectivity. Therefore, total inactivation cannot be reached with certainty. Viral-inactivating chemical agents include: lipid solvents (effective against enveloped but not naked virions), alkylating agents, e.g. ethylene oxide (effective against all virions); lipolytic enzymes (for some enveloped virions).
A variety of germicides are on the market because of patent rights. For example, Canadian patent 1,290,243 issued 8 Oct. 1991 to Thomas AUCHINCLOSS, is directed to a germicide composition comprising five ingredients: an inorganic halide (sodium chloride), an oxidising agent (potassium persulfate triple salt), sulfamic acid, an organic acid (malic acid), and an anhydrous alkali metal phosphate. Enhancement of the virucidal activity of the germicidal composition is claimed, due to alleged buffering and chelating effect of the alkali metal phosphate.
The AUCHINCLOSS patent relates to biocidal (bacteria, fungi, et al) and virucidal compositions. However, a number of drawbacks have been discovered by applicant with respect to such a germicide compound:
(a) it is not effective against bacterial and fungi spores;
(b) because it is based on the release of chlorine in contact with an oxidizing agent and with non reducible organic acids, it remains of limited scope of activity;
(c) because of the presence of chlorine ions in sewage, it may give rise to organochlorine derivatives (carcinogenic compounds) and therefore, is undesirable in sewage water;
(d) the release of phosphates by the biocidal compound will pollute sewage water, and again for this reason is undesirable in waste water;
(e) sodium alkyl sulfate linear, a high foaming agent, is also undesirable in sewage water, since it will substantially reduce the efficiency of the waste water treatment plants;
(f) the lowermost pH level obtained after use of the biocidal composition is not acid enough to meet actual standards of sewage water pH.